I have five, two foot tall bushy sativa plants sitting under my 1000 watt. My landlord came by and freaked out but I showed him that I had a medical card and I have had some back issues so he says "crop then you have to stop." lol he's such a hippy always a chill dude. Well he told me that the plants will double or triple in size by harvest which means something under 72 inches. Which is pretty fuckin tall. Does that sound right? 4 ft tall plants to me seem fairly big.
Ahhh the days of the first grow.... marijuana plants often will double to triple in size but not always. Considering they are sativas, do expect for a lot of stretching. Btw there's a grow section check it out and post there next time.